my scrape brush is weird
ok when there are parts of your mesh with more depth of detail this bug happens, because the detail size that you are using its more bigger than the detail size that containts in that area or part of the mesh, so to fix it change the detail size to the proper size that was used in that area. nevertheless with this "bug" (its not a bug actually) you can easily optimize your mesh if it gets too over loaded of polygons for example. also if you dont see anything happen, just add some geometry with the sculpt draw brush and then use the scrape brush in that area again.